Navegando por Autor "Cobuci, Jaime Araujo"

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    Breed, heterosis, and recombination effects for lactation curves in Brazilian cattle
    (2021) Daltro, Darlene dos Santos; Padilha, Alessandro Haiduck; Gama, Luís Telo da; Silva, Marcos Vinícius Gualberto Barbosa da; Cobuci, Jaime Araujo
    ABSTRACT The objective of this study was to estimate the breed, heterosis, and recombination effects on different components of the lactation curve of Girolando cattle. The dataset used consisted of 12,121 purebred cows of Holstein (H) and Gyr (G) breeds, and six H×G crossbred cows (Girolando). The model used presents random effects of herd and cow, regression coefficient associated with linear effect of proportion of H breed, regression coefficient associated with the linear effect of heterosis between H and G breeds, regression coefficient associated with the linear effect of recombination between H and G breeds, and random effect of residual. Dijkstra's (DJ), Nelder's (ND), Wilmink's (WL), and Wood's (WD) models were tested to fit production records of these different genetic groups. These models were then tested according to evaluation criteria of quality of fit (AIC, BIC, and RMSE), and the two best models (WD and WL) were chosen for estimation of 305-day milk yield (MY305), peak yield, time to peak, and persistency of milk yield. The breed effect was significant for all traits and components of the lactation curve. The heterosis effect was significant for all traits, and was more significant for MY305 (945.62±79.17 kg). Peak yield was the component of lactation curve that presented the most significant heterosis effect, partially explaining the heterosis effect (12 to 21%) found for MY305. The recombination effect was positive only for lactation period and time to peak of lactation in Girolando cows.
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    Estimativas de tendência genética para características produtivas em um rebanho do ecótipo Mantiqueira
    (2001) Silva, Marcos Vinícius Gualberto Barbosa da; Ferreira, William José; Cobuci, Jaime Araujo; Guaragna, Guilherme Paes; Oliveira, Paulo Rogério Palma de
    The data used in this study are from the first five lactations of 1,406 cows of the Mantiqueira Ecotype, daughters of 113 sires, with calving from 1952 to 1997. The total milk yield (PL), fat production (PG), lactation period (DL), and days dry (PS) were obtained from NPZGJRA/IZ/APTA/SAA. Based on the genetic values predictions, for each studied feature selection differentials and genetic trends were estimated though four selection paths of selection: bulls to breed bulls (SB), cows to breed bulls (DB), bulls to breed cows (SC) and cows to breed cows (DC). Two periods were involved: the first, from 1952 to 1976, representing the formation period and herd increase, the second, from 1977 to 1997, when the breeding program was implemented. The whole period from 1952 to 1997 was also considered. MTDFREML was used in the analysis with an animal model containing the year-season effects of calving, lactation period, the linear and quadratic effects of age of calving as fixed effects. Animal and permanent environment and error were included as random effects. The selection differentials for the SB and SC paths were larger in the first period. DB and DC paths were larger in the second period due to changes in the selection criterion. Selected gains for PG, DL, and PS paths were very small suggesting that the selection was only for PL. Rates of gains could be increased with changes in the breeding program. Os registros utilizados neste estudo foram provenientes das cinco primeiras lactações de 1406 vacas do ecótipo Mantiqueira, filhas de 113 reprodutores, com partos entre os anos de 1952 e 1997. As informações sobre as características produção total de leite (PL), produção de gordura (PG), duração da lactação (DL) e período seco (PS) foram obtidas do NPZGJRA/IZ/APTA/SAA. Com base nas predições dos valores genéticos, para cada característica estudada, estimaram-se os diferenciais de seleção e as tendências genéticas, por meio de quatro trajetórias de seleção: touros pais de touros (SB), vacas mães de touros (DB), touros pais de vacas (SC) e vacas mães de vacas (DC). Os períodos estudados compreenderam os anos de 1952 a 1976, primeiro período, que representou a formação e a ampliação do rebanho; de 1977 a 1997, segundo período, caracterizado pela implementação de um programa de melhoramento genético do ecótipo; e de 1952 a 1997, período total. As análises foram feitas por meio do sistema MTDFREML, com um modelo animal que incluiu os efeitos fixos de ano-estação de parto e duração da lactação e, como covariável, a idade da vaca no parto, em meses, com termos linear e quadrático. Como efeitos aleatórios foram incluídos animal, efeito permanente de meio e erro. Verificou-se que os diferenciais de seleção das trajetórias SB e SC foram superiores aos das demais trajetórias, no primeiro período, enquanto no segundo período, no entanto, em razão da mudança de critério de seleção, os diferenciais de seleção das trajetórias DB e DC foram maiores. As tendências genéticas obtidas para PG, DL e PS foram inexpressivas, o que sugere que a seleção tenha sido direcionada somente para PL. As taxas de ganho genético podem ser aumentadas, razão pela qual o programa de melhoramento deve ser reestruturado.